1. Field of the Invention
The present invention relates to a method for fermentation of a biodegradable or fermentable refuse slurry comprising causing household refuse, organic industrial waste, animal manure or the like to ferment into an odorless fertilizer and an apparatus for manufacture of an organic fertilizer from such refuse.
2. Brief Description of the Prior Art
The technique of aerobic fermentation of a biodegradable refuse slurry to produce an odorless fertilizer has been implemented using various systems. For example, Japanese Patent Publication No. 55-29958 discloses a fluidized-bed technique which comprises charging a horizontal rotary cylinder in a vertically splittable casing with a fermentable refuse slurry whose water content has been adjusted with saw dust and introducing warm air into the cylinder to cause fermentation. Japanese Patent Publication No. 55-32680 discloses a fixed-bed technique comprising feeding a fermentable refuse slurry into a stationary wire-mesh vessel disposed in a casing and having a plurality of wire-mesh cylinders extending vertically from the bottom thereof and feeding air from the bottoms of said cylinders upwardly to cause fermentation.
Regarding the latter fixed-bed technique, one of the inventors of the present invention previously proposed an improvement in Japanese Kokai Patent Publication No. 63-201082, which offers an increased efficiency of aerobic fermentation and a facilitated withdrawal of the fermentation product.
In this improved system, the starting material to be fermented is fed from the top of the vessel via a conveyer or the like and, after fermentation, the bottom plate of the vessel is swung open downwardly to effect withdrawal of the product of fermentation en bloc. The fermentation vessel is internally provided with a plurality of air supply pipes each having a multiplicity of air outlets and each of these air supply pipes is rigidly secured to a plate extending from the inner wall of the vessel at 2 or 3 levels by means of saddle bands or the like. The lower end of the pipe communicates with a corresponding hole drilled in the bottom plate so that feed air (warm air) may be blown into the pipe through said hole. Thus, the bottom of the vessel is comprised of two bottom plates and as the warm air is supplied to the enclosed space between the two bottom plates, it is fed into the interior of the vessel through said holes in the upper bottom plate and said air supply pipes. The spent air is exhausted from exhaust holes in the upper lid. As the charged slurry is fermented, the internal temperature of the vessel is increased and heavily moisture-laden warm air is exhausted.
While the above equipment accomplished its objects fairly well, the following problems remained to be solved yet.
(1) In withdrawing the fermentation product from the fixed-bed equipment, the fermentation product compacted and bridging the plural air supply pipes does not fall smoothly even when the bottom plate of the vessel is open wide and it is necessary for the operator to wait for some time until the gravity discharge has been completed or push the product down with a rod or the like from the top opening. Thus, it takes much labor and time to withdraw the fermentation product.
(2) Polyvinyl chloride pipe is generally used for the air supply pipes from the consideration of corrosion resistance and equipment cost but since the lower end of each air supply pipe is supported in alignment with the hole in the bottom plate, the pipe tends to be bent on charging the vessel with the material to be fermented or deformed by heat so that the alignment between the lower end of the pipe and the hole in the bottom plate is sometimes disturbed so as to prevent the proper air supply.
(3) Because the air supply pipes are used exclusively for supplying air, there is substantially no air flow in the direction from one pipe to another, with the air being fed only to the vicinity of each pipe. Moreover, because the upper part of the fermentation vessel is supplied with a comparatively larger amount of air than is the lower part, no uniform supply of air could be insured throughout the whole fixed bed.
Furthemore, just because of the structural characteristic of the equipment that the warm air is not directly fed to the air supply pipes within the vessel but is first fed to the space between the upper and lower bottom plates and, then, supplied to the respective air supply pipes, the loss of heat is fairly large and the cost of operation is as much increased.
(4) Though it depends on the fermentation load to be dealt with, generally a plant is made up of 3 or more fermentation vessels. Then, each fermentation vessel differs from the other vessels in the status of fermentation, so that the internal temperature also varies from one vessel to another.
For a fermentation vessel where a low temperature prevails, warm air must be supplied to expedite the fermentation reaction, while no warm air is needed in the vessel where a high temperature prevails. Moreover, although the temperature of exhaust air from the latter vessel is also high, the exhaust air is directly exhausted without reclaiming its heat, while the feed air is constantly heated.
(5) In the above fermentation system, fermentor temperature control and supply/exhaust air flow control depend much on experience and require frequent check of the fermentation process, for example by reference to readings of temperature sensors installed with the vessel.